1. Field of the Invention
The present invention relates to a semiconductor light emitting device, and more particularly, to a method of manufacturing a nitride-based semiconductor light emitting device having an improved structure in which optical extraction efficiency is improved.
2. Description of the Related Art
Light emitting devices, such as light emitting diodes (“LEDs”), are generally semiconductor p-n junction diodes. Silicon p-n junctions continue to play a leading role in the electronic information revolution, and p-n junctions of a group III-V semiconductor continue to play a leading role in the optical revolution away from traditional incandescent or fluorescent light sources and toward LED-based lighting. Group III-V semiconductors are made by combining group III and group V elements, also referred to as group 13 and group 15 elements. They have an advantage of a luminous efficiency that is almost 100%. The luminous efficiency of these materials is approximately one thousand times higher than that of silicon. Thus, starting from the initial stage of development of a material, LEDs are widely used in light emitting devices such as diode lasers, and therefore play a leading role in the development of devices arising at the forefront of the optical revolution. In addition, since LEDs have a higher movement speed of electrons and can operate at a high temperature, they are widely used in high-speed and high-power electronic devices. In particular, several group III and group V elements are mixed with one another so that a semiconductor having a variety of material compositions and accompanying characteristics can be manufactured.
As basic characteristics of an LED, luminosity (units: candela (“cd”)) is used to describe an LED that emits in the visible region of the electromagnetic spectrum, and radiant flux (units: watt) is used to describe an LED that emits in the invisible region of the electromagnetic spectrum. Luminosity is measured as light velocity per unit cubic angle, and brightness is measured as luminosity per unit area. A photometer is used to measure luminosity. Radiant flux represents all power radiated from all wavelengths of an LED and is measured in energy radiated per unit time.
Main factors for determining the performance of a visible ray LED are luminous efficiency, measured in lumens per watt (Im/W). This measure corresponds to a wall-plug efficiency (i.e., total electrical to optical output power efficiency) that takes into consideration the response of the human eye to the luminosity of a light source. Luminous efficiency of an LED can be mainly determined by three factors: internal quantum efficiency, extraction efficiency, and operating voltage. Research into improvement of luminous efficiency is currently underway.
In general, conventional LEDs have a sapphire/n-GaN/MQW/p-GaN structure, wherein “MQW” is the multi-quantum well. However, in such LEDs, defect density is high due to limitations of manufacture technology. Thus, limitations to be addressed in the current technical objectives include improving internal quantum efficiency of an MQW layer, and manufacturing a high-power LED. Accordingly, and desirably, the structure of an LED should be improved so that the limitations can be overcome and external extraction efficiency of light can be increased.